Problems Flashread XC164 sector 5

Hello,
I am using XC164 and would like to read flash values wordwise.
All other Sectors can be read (0..4 does it fine), but on every access to sector 5 a controller hangup occurs.
Code is:

#define SECTOR_4 0xC08000
#define SECTOR_5 0xC10000
// tried to use local as well as global definition:
unsigned int huge* flashptr_Start;

  flashptr_Start = SECTOR_5;
  for (i = 0; i <= 0xFF; i++)
{
  siVal = (*(flashptr_Start)) & 0xFFFF;
  _nop_();_nop_();_nop_();_nop_(); // wait
  flashptr_Start++;
}

I don't see anything wrong with that piece of code. I tried to slow down (sfr IMBCTR) the flash access read time but it didnt help.

Did anyone get similar problems?
Can anyone help me?

Thanks in advance,
Helmut